In-phase Response Research Articles

DEM analysis on diffuse failure of soil slope triggered by earthquakes

Earthquake-induced diffuse landslide can cause considerable harm. This study used discrete element modeling (DEM) to investigate the diffuse failure of soil slopes triggered by earthquakes. Initially, the DEM was validated through demonstrating satisfactory agreement with the experimental results of a shaking table test. Subsequently, the time and most realistic location of diffuse failure occurrence was quantified using discrete second-order work. Diffuse failure was associated with abrupt fluctuation of the second-order work and a local burst of kinetic energy. Within the context of second-order analysis, the frictional resistance of the slope was analyzed. Both the in-phase and the out-of-phase evolutions of frictional resistance and seismic loading were captured. The distinctive in-phase response was identified as an important feature of diffuse failure. Moreover, the predominant influence of particle rolling behavior on frictional resistance development during diffuse failure progression was highlighted. The magnitude and anisotropy of the contact force are profoundly influenced by the input vibration amplitude, resulting in variations in frictional resistance, which suggests that stress-induced anisotropy plays a crucial role in diffuse failure. The results of this study shed light on the grain-scale failure mechanisms of earthquake-induced landslides, and serve as the basis for elucidating the failure behavior of seismic-induced landslides.

Rheo-PIV study of slip effects on oscillatory shear measurements of a yield-stress fluid

The influence of apparent slip on oscillatory shear measurements of a viscoplastic microgel [0.6 wt. % of poly(acrylic acid)] is analyzed by Couette and parallel-plate rheometry and particle image velocimetry (Rheo-PIV). We first provide direct evidence of a critical shear stress for the onset of slip of the microgel under oscillatory (σos) and nonoscillatory measurements (σs). Afterward, we describe the effect of slip on oscillatory measurements via waveforms, Bowditch–Lissajous curves, Fourier transform (FT) rheology, PIV, and as a sequence of physical processes (SPP). The effect of slip is mainly observed at low oscillating frequencies. For amplitudes of the oscillating stresses σ0 ≤ σos, the microgel exhibits linear viscoelastic behavior with in-phase strain response. For σos < σ0 ≤ yield stress (σy), slip introduces a phase shift in the strain response with a forward-tilted waveform and “mango” shape Bowditch–Lissajous curves. Meanwhile, FT rheology shows negligible even harmonics. The strain measured by the rheometer does not match the true strain determined by PIV in the presence of slip, resulting in waveforms that depend on how the displacement distribution is interpreted. This result indicates a break in the symmetry of the flow, that is, the microgel response no longer follows the imposed oscillation, which makes any attempt to correct oscillatory data for slip complex. This behavior arises from recoil of the slipping microgel after reaching its maximum displacement in a cycle. Finally, we provide an overall picture of the kinematics of the process of yielding in the presence of slip as an SPP.

3-D imaging of whole-space environments with electromagnetic induction sensors based on linear approximation

Accurate mapping of the periphery of tunnel has become an essential step in underground mining and engineering. Because of high sensitivity to electric conductivity and magnetic permeability, the whole-space electromagnetic (EM) method has played an important role in geological forecast of groundwater and exploration of mineral ore. However, obtaining a three-dimensional (3-D) image of the whole-space EM method by 3-D inversion is challenging due to the limited observation space and inefficiencies in 3-D forward modeling algorithms. While 1-D inversion algorithms have long been used to map the periphery of the tunnel, various 3-D inversion algorithms have been successfully applied in other scenarios. Recently, the portable frequency domain loop-loop EM induction (EMI) measurement has been considered as an active source magnetic method in near surface surveys, because of the dominance of magnetic permeability in the in-phase (IP) response. The 3-D linear forward modeling method is developed based on the location-specific magnetic sensitivity function, and the 3-D inversion algorithm has been effectively employed for mapping magnetic anomalies in large-scale area. In this study, we intend to demonstrate that the EMI measurement can give 3-D image of the periphery of the tunnel by theory and numerical experiments. The IP response of EMI in whole-space is separated into three parts, and the 3-D linear forward modeling method is examined by analytical solution. The 1-D Fourier transform is used to accelerate the 3-D forward modeling, and the 3-D inversion show a good performance of mapping the magnetic abnormal bodies in underground space.

Asymmetric flapping of a multi-segmented elastic structure

Motivated by the propulsion of animals using articulated bodies, this study experimentally investigates the deformation and torque generation of a multi-segmented structure undergoing flapping motion. The segmented structure consists of multiple rigid segments connected in a line through elastic sheets functioning as elastic hinges. To enhance the asymmetry in the deflection of the segmented structure between the power and recovery strokes, the elastic hinges are designed to bend only one way from their original position. To characterize the deflection profile of the segmented structure, new definitions are proposed for the effective bending stiffness of the entire structure and the dimensionless speed representing the relative magnitude of the fluid force acting on the structure to its internal bending force. These two quantities are used to determine the tip deflection adjusted by the discrete profile. Two typical deflection responses during the recovery stroke are identified, namely, an in-phase response and a delayed response. The difference in these deflection responses causes substantial changes in torque and thrust generation, particularly during the early stage of the subsequent power stroke. An evaluation of the torque and thrust generation performance, in terms of the net cyclic value and the degree of asymmetry between the two strokes, reveals the optimal model design and operation conditions of the segmented structure.

Improvement of Wind-Induced Responses of Twin Towers Using Modal Substructure Method with Link Bridges

A new wind-resistant design optimization method for twin towers by utilizing link bridges, named as the Modal Substructure (MSS) method, is proposed. The MSS method combines the benefits of engineering design approaches and theoretical analysis methods to achieve efficient wind-induced vibration control tailored to specific twin tower projects. The method involves three main steps: (1) establishing control objectives based on the wind-induced response characteristics of the twin towers, (2) determining control strategies by analyzing the modal acceleration characteristics of the twin towers, and (3) performing parameter optimization of the link bridge, including assessing the damping ratio, mass ratio, and frequency ratio of the bridge. By applying the MSS method, optimal configurations for the link bridge can be identified, leading to effective vibration reduction effects. The wind-induced responses of the twin towers exhibit three distinct types: predominance of out-of-phase response, predominance of in-phase response, and equal importance of in-phase and out-of-phase responses. Each response type necessitates the implementation of specific control strategies. We propose a two-section link bridge design approach: the upper section functions as a tuned mass damper to effectively control the in-phase response, while the lower section is designed as a “stiffness + damping component” to reduce the out-of-phase response.

Hydrological control shift from river level to rainfall in the reactivated Guobu slope besides the Laxiwa hydropower station in China

Landslides are common geohazards associated with natural drivers such as precipitation, land degradation, toe erosion by rivers and wave attack, and ground shaking. On the other hand, human alterations such as inundation by water impoundment or rapid drawdown may also destabilize the surrounding slopes. The Guobu slope is an ancient rockslide on the banks of the Laxiwa hydropower station reservoir (China), which reactivated during the reservoir impoundment in 2009. We extracted three-dimensional surface displacements with azimuth and range radar interferometry using European Space Agency's Copernicus Sentinel-1 and German Aerospace Center's TerraSAR-X data during 20152019. The upper part of the Guobu rockslide is characterized by toppling and is mostly subsiding with maximum rates over 0.4 m/yr and 0.7 m/yr in the vertical and horizontal directions, respectively. During filling of the reservoir prior to 2014, there was a long-wavelength in-phase response between rising reservoir level and GPS-observed increased slope movements. After the reservoir water level stabilized from 2015 to 2019, the slide movement became seasonal and we see a correlation between rainfall and landslide movement. These observations suggest that the slide motion is now primarily controlled by rainfall. The spatiotemporal landslide displacements allow us to estimate the hydraulic diffusivity of the rock mass, to be on the order (~1.05 × 10‐7 m2/s) and the thickness of the moving rock mass (~200 m). Our results demonstrate that InSAR is a useful tool for monitoring the rockslide movement as a function of seasonal precipitation.

Application of VLF-EM method for base metal exploration in Gwani area (Misau 107), Jigawa state, Nigeria

The Very Low Frequency (VLF) electromagnetic (EM) survey is a reliable technique for identifying network of fractures usually hidden by overburden materials that overlie the crystalline basement. The Gwaram area, Jigawa state of Nigeria is underlain by Older Granite of the basement complex of Nigeria, with predominant rock type being coarsely porphyritic biotite granite. The project is aimed at confirming the occurrence of sulphide mineralization within the study area, using both the geological information and VLF techniques. Measurements involving 10 profiles spaced 50 m interval were collected within the study area, using the transmitter of Le Blanc in France whose radio frequency is 18.3 kHz. Profiles 1-10 show the respective cross-over points (points of intersection) at 430, 460, 430, 470, 480, 500, 550, 560, 610, and 620 m with a positive in-phase response of 11.1, 7.3, 22.1, 23.7, 30.8, 36.2, 29.5, 17.6 and 20.8% respectively, the suspected fault occurred at respective depth of 45, 130, 150, 135, 150, 135, 140, 145, 145 and 125 m. The ratios of primary to secondary electromagnetic anomalies on the ten profiles are not constant and their profile shapes are never identical or consistent. Such anomalies at cross-over points have been used to infer the presence of fracture. All the profiles show one identical anomaly which is suspected to be a hydrothermal zone or mineralized fault. VLF-EM contour and 3D map were produced and indicate that there is high conductivity toward the southwest of the map. The results obtained in the survey inferred that the deposit is expected to be economically viable.

3-D imaging of subsurface magnetic permeability/susceptibility with portable frequency domain electromagnetic sensors for near surface exploration

SUMMARY The in-phase response collected by portable loop–loop electromagnetic induction (EMI) sensors operating at low and moderate induction numbers (≤1) is typically used for sensing the magnetic permeability (or susceptibility) of the subsurface. This is due to the fact that the in-phase response contains a small induction fraction and a preponderant induced magnetization fraction. The magnetization fraction follows the magneto-static equations similarly to the magnetic method but with an active magnetic source. The use of an active source offers the possibility to collect data with several loop–loop configurations, which illuminate the subsurface with different sensitivity patterns. Such multiconfiguration soundings thereby allows the imaging of subsurface magnetic permeability/susceptibility variations through an inversion procedure. This method is not affected by the remnant magnetization and theoretically overcomes the classical depth ambiguity generally encountered with passive geomagnetic data. To invert multiconfiguration in-phase data sets, we propose a novel methodology based on a full-grid 3-D multichannel deconvolution (MCD) procedure. This method allows us to invert large data sets (e.g. consisting of more than a hundred thousand of data points) for a dense voxel-based 3-D model of magnetic susceptibility subject to smoothness constraints. In this study, we first present and discuss synthetic examples of our imaging procedure, which aim at simulating realistic conditions. Finally, we demonstrate the applicability of our method to field data collected across an archaeological site in Auvergne (France) to image the foundations of a Gallo-Roman villa built with basalt rock material. Our synthetic and field data examples demonstrate the potential of the proposed inversion procedure offering new and complementary ways to interpret data sets collected with modern EMI instruments.

Toward subsurface magnetic permeability imaging with electromagnetic induction sensors: Sensitivity computation and reconstruction of measured data

In near-surface geophysics, small portable loop-loop electromagnetic induction (EMI) sensors using harmonic sources with a constant and rather small frequency are increasingly used to investigate the electrical properties of the subsurface. For such sensors, the influence of electrical conductivity and magnetic permeability on the EMI response is well-understood. Typically, data analysis focuses on reconstructing an electrical conductivity model by inverting the out-of-phase response. However, in a variety of near-surface applications, magnetic permeability (or susceptibility) models derived from the in-phase (IP) response may provide important additional information. In view of developing a fast 3D inversion procedure of the IP response for a dense grid of measurement points, we first analyze the 3D sensitivity functions associated with a homogeneous permeable half-space. Then, we compare synthetic data computed using a linear forward-modeling method based on these sensitivity functions with synthetic data computed using full nonlinear forward-modeling methods. The results indicate the correctness and applicability of our linear forward-modeling approach. Furthermore, we determine the advantages of converting IP data into apparent permeability, which, for example, allows us to extend the applicability of the linear forward-modeling method to high-magnetic environments. Finally, we compute synthetic data with the linear theory for a model consisting of a controlled magnetic target and compare the results with field data collected with a four-configuration loop-loop EMI sensor. With this field-scale experiment, we determine that our linear forward-modeling approach can reproduce measured data with sufficiently small error, and, thus, it represents the basis for developing efficient inversion approaches.

Low signal-to-noise FDEM in-phase data: Practical potential for magnetic susceptibility modelling

In this paper, we consider the use of land-based frequency-domain electromagnetics (FDEM) for magnetic susceptibility modelling. FDEM data comprises both out-of-phase and in-phase components, which can be related to the electrical conductivity and magnetic susceptibility of the subsurface. Though applying the FDEM method to obtain information on the subsurface conductivity is well established in various domains (e.g. through the low induction number approximation of subsurface apparent conductivity), the potential for susceptibility mapping is often overlooked. Especially given a subsurface with a low magnetite and maghemite content (e.g. most sedimentary environments), it is generally assumed that susceptibility is negligible. Nonetheless, the heterogeneity of the near surface and the impact of anthropogenic disturbances on the soil can cause sufficient variation in susceptibility for it to be detectable in a repeatable way. Unfortunately, it can be challenging to study the potential for susceptibility mapping due to systematic errors, an often poor low signal-to-noise ratio, and the intricacy of correlating in-phase responses with subsurface susceptibility and conductivity. Alongside use of an accurate forward model – accounting for out-of-phase/in-phase coupling – any attempt at relating the in-phase response with subsurface susceptibility requires overcoming instrument-specific limitations that burden the real-world application of FDEM susceptibility mapping. Firstly, the often erratic and drift-sensitive nature of in-phase responses calls for relative data levelling. In addition, a correction for absolute levelling offsets may be equally necessary: ancillary (subsurface) susceptibility data can be used to assess the importance of absolute in-phase calibration though hereby accurate in-situ data is required. To allow assessing the (importance of) in-phase calibration alongside the potential of FDEM data for susceptibility modelling, we consider an experimental test case whereby the in-phase responses of a multi-receiver FDEM instrument are calibrated through downhole susceptibility data. Our results show that, while it is possible to derive approximate susceptibility profiles from FDEM data, robust quantitative analysis hinges on appropriate calibration of the responses.

Characterization of buried cables and pipes using electromagnetic induction loop-loop frequency-domain devices

The detection and characterization of buried cables and metal pipes has become a key component of field surveys carried out prior to excavation work on construction sites. The very high conductivity and magnetic permeability contrast between any buried cables/pipes compared with the soil makes electromagnetic induction (EMI) instruments very useful for their detection. We have developed a seminumerical method that can be used to model the responses of this type of target. A straight horizontal conductor is equivalent to a series of magnetic dipoles, the magnitude of which can be determined in the spectral domain and then converted back into the spatial domain through the use of an inverse fast Fourier transform. Simulations and case studies allow to establish rules of thumb for the estimation of (1) the nature of the metal: the in-phase response of magnetic cables is of the opposite sign from the conducting ones, (2) the sensitivity to the target characteristic: the influence of the cable/pipe diameter is greater than that of the metal properties, and (3) the depth of the cables. The simulations also underline the role of the coil configuration: Vertical coplanar and perpendicular responses allow a more precise location of the cable/pipe, whereas the horizontal coplanar response is less dependent on the orientation. As ground truth, a known electric cable buried at a depth of 0.5 and 0.002 m in diameter is determined at 0.56 m. The first field test is related to the detection of a buried military cable from World War I, between 2.5 and 3 m below the original ground level. The second field test is related to the detection of a water pipe 0.35 m deep. The modeling technique can be applied to all EMI prospecting methods, and thus it opens the way to the correction of the disturbances generated by cables and pipes.

Detecting anomaly targets using handheld frequency domain electromagnetic system

In this paper, a handheld frequency domain electromagnetic system CEM-2 is presented for subsurface investigation (within less than 2m). CEM-2 system employs one set of 3 coplanar coils. The transmitter uses sinusoidal pulse width modulation technology to generate low total harmonic distortion and arbitrary digital signal waveform. It is convenient to match different transmitting coils using the same circuit and system. The signal processing method can reduce some effects caused by unstable factors. Most operations are sum and product operation, contributing to high efficiency. The mounting positions of the metal items (a removable box, pre-amplifier) are selected according to the principle that primary magnetic field has minimum gradient. Experiments were conducted to evaluate the CEM-2 system. The response decreases as the operation frequency increases. The in-phase response changes with frequency faster than quadrature response. When the major axis of a target is in parallel with the system, the response is the strongest while the response is the weakest when the target is perpendicular to the system. This is because the effective conductivity is different due to de-polarization factor under primary field from different incident direction. Furthermore, results in a simulated test site indicate that CEM-2 can give distinct signatures for abnormal targets.

Ultra-low temperature ac susceptibility of the heavy-fermion superconductor YbRh2Si2

Recently, we reported on the discovery of superconductivity in YbRh2Si2 at the very low temperature Tc = 2 mK. We present here complementary measurements of the temperature and field dependence of the ac susceptibility χac (T) of this heavy-fermion system for temperatures down to 1 mK and magnetic fields in the basal plane up to 75 mT. The in-phase response shows a steep drop at Tc, but it does not become negative, possibly because of the presence of the earth field that was not compensated. The out-of-phase response shows an increase right below Tc indicating that the transition is first order. We also observe two kinks in the field dependence of χac(B) at B1 ≈ 50 mT and B2 ≈ 60 mT, which imply a more complex T – B phase diagram for YbRh2Si2 with B ⊥ c. These features possibly indicate two second-order phase transitions or domain reorientation at B1 and a phase transition from the antiferromagnetic to the paramagnetic state at B2.

Temperature-dependent hysteresis effects on EM induction instruments: An example of single-frequency multi-coil array instruments

Non-invasive electromagnetic (EM) induction has been used in agriculture, earth science and archaeology. This is because the apparent electrical conductivity (ECa or quadrature response – mSm−1) and the apparent magnetic susceptibility (in-phase response – ppt) which they measure are related to soil properties such as clay, soil mineralogy, salinity and soil moisture as well as buried metal objects. Although the accuracy issues of the single-coil array EM38 meter have been widely discussed, the accuracy issues of the next generation, multi-coil (perpendicular-PRP and horizontal-HCP) array DUALEM meter, particularly the instrument drift, have little been reported. In this study, the diurnal drifts of a DUALEM-421S and a DUALEM-21S were studied at single locations (for a 24h period) and along a 480-m transect (at five typical operation times). Based on the experiment results of the two DUALEM instruments, it was found that the ECa readings of the PRP arrays were more stable than those of the HCP arrays. The reverse was true for in-phase measurements. Specifically, during the diurnal cooling and heating phases, ECa measurements of the HCP arrays and in-phase PRP arrays showed different correlations with ambient temperature, which can be defined as instrument-specific and temperature-dependent hysteresis effects. In addition, the stability of ECa and in-phase measurements increased with array length and was much less compared to the theoretical values. It was suggested a similar experiment should be conducted for the DUALEM instruments before the DUALEM surveys and repeated DUALEM surveys for mapping the spatio-temporal variations in soil properties should be carried out at the similar temperature (i.e., similar ambient temperature and within the same warming or cooling phase). In addition, shading the instruments with non-conductive thermal insulation should be adopted and drift correction procedures should be applied to improve the quality of the measurements of the EM instruments.

Lasing and anti-lasing in a single cavity

Using Parity-time symmetry, we experimentally realize lasing and anti-lasing at the same equency in a single cavity. Because of the time-reversal property, the demonstrated lasing and anti-lasing resonances share common resonant features such as identical frequency dependence, coherent in-phase response and line spectral resolution. Lasing and anti-lasing in a single device offers a new route for light modulation with high contrast approaching the ultimate limit.

Quasi-biennial oscillation signal detected in the stratospheric zonal wind at 55–65°N

AbstractTo investigate the impacts of the quasi-biennial oscillation (QBO) on high-latitude circulation and the Arctic vortex, stratospheric zonal wind at 55–65°N is analyzed. The seasonal cycle, solar cycle, and linear trend in the zonal wind at these latitudes are analyzed and removed, and the QBO signal is retrieved from the monthly zonal wind for the period 1979–2014. The zonal wind has a strong decreasing trend in winter, with a maximum decrease (less than −0.35 m s−1 yr−1) occurring within 70–100°E. The zonal wind has an in-phase response of 1.6 m s−1 to the solar cycle, with a maximum within 100–140°E. A clear QBO signal is detected in the zonal wind during the period 1979–2014, with an amplitude of 2.5 m s−1 and a period of 30 months. The latitudinal distribution of the QBO signal is inhomogeneous, with a maximum within 120–180°E and a minimum within 25–45°E.

Micromechanical finite element modelling of thermo-mechanical fatigue for P91 steels

In this paper, the cyclic plasticity and fatigue crack initiation behaviour of a tempered martensite ferritic steel under thermo-mechanical fatigue conditions is examined by means of micromechanical finite element modelling. The crystal plasticity-based model explicitly reflects the microstructure of the material, measured by electronic backscatter diffraction. The predicted cyclic thermo-mechanical response agrees well with experiments under both in-phase and out-of-phase conditions. A thermo-mechanical fatigue indicator parameter, with stress triaxiality and temperature taken into account, is developed to predict fatigue crack initiation. In the fatigue crack initiation simulation, the out-of-phase thermo-mechanical response is identified to be more dangerous than in-phase response, which is consistent with experimental failure data. It is shown that the behaviour of thermo-mechanical fatigue can be effectively predicted at the microstructural level and this can lead to a more accurate assessment procedure for power plant components.

Two wind-driven modes of winter sea ice variability in the Barents Sea

The interannual variability of the winter sea ice area in the Barents Sea is investigated using SMMR-SSM/I data and a coupled ocean–sea ice model over the period 1979–2012. Our analysis reveals that the sea ice area in the northern and eastern parts of the Barents Sea do not covary. This contrast in behavior allows us to associate two distinct modes of variability with these two regions, with the variability of the overall Barents Sea ice cover being predominantly captured by the northern mode. Both modes show a dominant, near in-phase response to the surface wind, both being associated with different spatial patterns. The northern mode emerges in response to northwesterly wind anomalies which favor the export of ice and surface polar water from the Arctic between Svalbard and Franz Josef Land. Atlantic Water temperature anomalies, formed concomitantly with northerly wind anomalies in the vicinity of the Barents Sea Opening, also influence the northern mode in the following winter. These temperature anomalies are linked to local convergence of the oceanic heat transport. The delayed influence of the ocean on the sea ice is found primarily in the northeastern Barents Sea and occurs through the re-emergence of the Atlantic water temperature anomalies at the surface in the following fall and winter. An ocean-to-atmosphere feedback initiated by October SST anomalies in the central Barents Sea is further identified. This feedback is hypothesized to enhance the sea ice response in the northern Barents Sea by promoting the formation of meridional wind anomalies. In contrast, the eastern mode of variability of the Barents Sea ice mainly responds to wind anomalies with a strong zonal component, and is less influenced by the Atlantic Water temperature variability than the northern mode. While our results clearly highlight a role of the ocean in the Barents Sea ice variability, this role appears to be more spatially restricted following the sudden northward retreat of the ice margin in 2004. In particular, the sudden drop in the sea ice area in 2004 could not be linked to earlier Atlantic water changes in the Barents Sea Opening.

AC Magnetic Susceptibility and Morphological Development of YBCO HTS Formed from Y:Ba:Cu = 1:2:3 and 3:5:8

Synthesis of superconducting YBCO sample after the earliest sintering stage was made possible by employing Y:Ba:Cu = 3:5:8 precursor ratios. Sintering temperatures used were in the range 840–950∘C. XRD well corresponds to YBCO structure. This study suggests that Y358 is a metastable state that requires the formation of Y123 in the early stages. Various morphological structures were obtained using different sintering profile and stoichiometric ratios. Morphology and AC magnetic susceptibility were correlated and compared to YBCO HTS formed using the standard Y:Ba:Cu = 1:2:3 ratios. The length of intra-to-intergranular in-phase response and the degree of out-of-phase (loss) peak shifting to lower temperature is highly dependent to the morphology and nature of grain boundaries. A good control in morphology by optimizing the temperature profile can address various applications such as in superconducting bulk magnets, films, and devices.

Frequency domain electromagnetic induction survey in the intertidal zone: Limitations of low-induction-number and depth of exploration

Subsurface investigation in the Belgian intertidal zone is severely complicated due to high heterogeneity and tides. Near-surface geophysical techniques can offer assistance since they allow fast surveying and collection of high spatial density data and frequency domain electromagnetic induction (EMI) was chosen for archaeological prospection on the Belgian shore. However, in the intertidal zone the effects of extreme salinity compromise validity of low-induction-number (LIN) approximated EMI data. In this paper, the effects of incursion of seawater on multi-receiver EMI data are investigated by means of survey results, field observations, cone penetration tests and in-situ electrical conductivity measurements. The consequences of LIN approximation breakdown were researched. Reduced depth of investigation of the quadrature-phase (Qu) response and a complex interpretation of the in-phase response were confirmed. Nonetheless, a high signal-to-noise ratio of the Qu response and viable data with regard to shallow subsurface investigation were also evidenced, allowing subsurface investigation in the intertidal zone.